In social networking, an internet mirage is when a user is offline or inactive but appears online or currently active to another computer. This only becomes apparent once the user of that computer attempts to communicate with them. Often, this leads to paranoid feelings of unpopularity, because the user erroneously assumes that the person left because they didn't want to speak to them.
Simon: "DAAVE my good mate, how're you doing?"
Computer: "David is now offline."
Simon: ":O What a douche!... oh wait, it was probably just an internet mirage... or was it?"